1. Field of the Invention
The present invention relates to a multi beam exposing device for focusing and irradiating, per pixel, each of beams emitted from a means for selectively turning on or off a plurality of pixels such as a spatial light modulator disposed in an exposing head based on image data (i.e., pattern data), with an optical element such as a lens array, so as to expose a predetermined pattern. The present invention also relates to an exposure method using the multi beam exposing device.
2. Description of the Related Art
In recent years, there has been developed a multi beam exposing device for subjecting a member to be exposed, to image exposure with an optical beam modulated in accordance with image data, by utilizing a spatial light modulator such as a digital micro mirror device (abbreviated as “a DMD”) as a pattern generator.
Such a DMD is a mirror device including numerous micro mirrors, the angle of the reflection surface of each being varied in response to, for example, a control signal, with the mirrors being arranged on a semiconductor substrate made of silicon or the like in a two-dimensional manner. The DMD is configured such that the angle of the reflection surface of the micro mirrors is varied by static electricity generated by electric charges accumulated in each of several memory cells.
In a conventional multi beam exposing device using a DMD, there is used, for example, an exposing head for collimating a laser beam emitted from a laser beam-emitting light source by means of a lens system, and reflecting each of the laser beams off the plurality of micro mirrors of the DMD that are arranged at substantially the focusing position of the lens system, so as to emit each of the beams from a plurality of beam emitting ports. Each of the beams emitted from the plurality of beam emitting ports in the exposing head is focused on the exposure surface of a photosensitive material (i.e., a member to be exposed) in a small spot diameter with a lens system having an optical element such as a micro lens array for focusing one beam per pixel with a single lens, thereby achieving image exposure with a high resolution.
In the above-described exposing device, the laser beam is modulated (i.e., deflected) by a controller, not shown, controlling the turning on or off of each of the micro mirrors in the DMD based on the control signal produced in accordance with image data or the like. Then, the exposure surface (i.e., recording surface) is exposed to the modulated laser beam by irradiation.
The exposing device is configured such that a photosensitive material (such as a photoresist) is disposed on the recording surface, and thereafter, that patternwise exposure can be performed on the photosensitive material by modulating each of the DMDs in accordance with the image data while moving the position of a beam spot relative to the photosensitive material, the beam spot being formed by irradiation of the laser beams from the plurality of exposing heads, respectively, in the multi beam exposing device on the photosensitive material.
In the case where the above-described multi beam exposing device is used in, for example, exposure of a circuit pattern on a substrate with high accuracy, there are instances where a relationship of precise similarity is not established between an image formed at the reflection surface formed by all of the micro mirrors in the DMD and an image projected at the exposure surface. This is a result of the lens for use in an illumination optical system or a focusing optical system in the exposing head having an inherent distortion characteristic. In other words, an image projected on the exposure surface may be deformed and deviate in position due to the distortion, and as a result, may not strictly match the designed circuit pattern.
In view of this, there has been proposed a means for correcting the distortion in a conventional exposing device. Such a means for correcting the distortion is adapted to set an origin at a predetermined position in the entire exposed region to be projected on a plotted surface with an exposing unit, to measure a relative position (i.e., an exposure point) of an optical image by a given micro mirror with specialized equipment before plotting, and to store the actual measurement value as exposure point coordinate data in the ROM of a system control circuit. In plotting, the actual measurement value is output as exposure point coordinate data to an exposure point coordinate data memory.
In this manner, bit data on the circuit pattern which has been substantially subjected to the distortion correction is stored in the exposure data memory. Therefore, since the exposure data to be given to each of the micro mirrors is a value with the distortion taken into account, the circuit pattern can be plotted with high accuracy even if there is distortion in the optical element in the exposing unit (see, for example, Japanese Patent Application Laid-Open (JP-A) No. 2003-57834).
In the above-described multi beam exposing device, the distortion of a plotted image caused by the exposing head varies with the lapse of time due to factors such as temperature and vibration when plotting with higher accuracy, and therefore, it is necessary to measure the distortion of a plotted image varying with the lapse of time each time before plotting with specialized equipment, so as to properly correct the distortion.